Maintaining and repairing mechatronic devices and systems

Operation Sheet 4.1.7: Guide for Sensor Installation

FURTHER INFORMATION:
The manufacturer is not liable for the improper use of the product.
Any use and/or application which are not provided for by the instruction manuals must be previously and directly
authorized by the same manufacturer.

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Operation Sheet 4.1.7: Guide for Sensor Installation

SENSITIVITY ADJUSTMENT FOR CAPACITIVE SENSORS:

1. Sensitivity adjustment should be carried out when the sensor is installed in a definitive and stable
position.

2. Adjustment should be fixed in an intermediate position between minimum and maximum because, since
air is a dielectric, a strong variation in humidity could cause inappropriate energizing of the sensor (if
adjustment is very fine).

3. The intervention range of the sensor depends on the type of material to be detected and its dimensions
(see reduction factor table). The distance can vary depending on the temperature variation by about ±
10% in a range of -20 to +70°C.

4. To increase sensitivity, turn the trimmer clockwise, to decrease sensitivity, turn it anti-clockwise.
5. To gain access to the trimmer, remove the plastic protection screw located at the back of the sensor.

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Operation Sheet 4.1.7: Guide for Sensor Installation

ELECTRICAL PARAMETERS

 NOMINAL VOLTAGE – Is indicates the maximum and minimum voltage values within which sensors
work correctly.

 RESIDUAL RIPPLE– Maximum admissible ripple of the DC supply voltage shown as percentage to its

medium value.
 MAXIMUM OUTPUT CURRENT – It shows maximum output current a sensor can cope with when

working steadily.
 MAXIMUM LEAKAGE CURRENT – Existing load current when output stage is stopped and supply

voltage is at maximum nominal value.
 ABSORPTION – This in the consumption of the photocell referred to the maximum limits of the nominal

voltage and without load.
 VOLTAGE DROP – Voltage drop on switching circuit when output transistor is conducting.
 SHORT CIRCUIT PROTECTION – A protection in case of short circuits or overload to avoid inner circuit

damage. Once the short circuit is eliminated the photocell resets.
 PROTECTION AGAINST INVERSION OF POLARITY– Available in DC supplied type, it prevents the

sensor from being damage when supply cables are incorrectly connected.
 INDUCTIVE LOAD PROTECTION – It protects sensor output in presence of high inductive loads.
 This protection is performed by a diode or zenner diode.
 PROTECTION DEGREE – It shows degree of protection of housing conform to EN60529 regulation.
 START UP DELAY – Time interval between sensor supply connection and active output. This time

interval is to avoid the switch output being in an undefined state when the system is switched on.
 RATED VOLTAGE – It indicates the power supply where the sensor works perfectly.
 MAXIMUM PEAK CURRENT– The maximum current the sensor can sustain in a limited period of time.

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

Learning outcomes:
5 Troubleshooting techniques.

Learning Activity:
5.1 Familiarize the general principles troubleshooting techniques.

TROUBLESHOOTING
Perhaps the most valuable but difficult-to-learn skill any technical person could have is the ability to troubleshoot a
system. For those unfamiliar with the term, troubleshooting means the act of pinpointing and correcting problems
in any kind of system. For an auto mechanic, this means determining and fixing problems in cars based on the
car's behavior. For a doctor, this means correctly diagnosing a patient's malady and prescribing a cure. For a
business expert, this means identifying the source(s) of inefficiency in a corporation and recommending corrective
measures.

Troubleshooters must be able to determine the cause or causes of a problem simply by examining its effects.
Rarely does the source of a problem directly present itself for all to see. Cause/effect relationships are often
complex, even for seemingly simple systems, and often the proficient troubleshooter is regarded by others as
something of a miracle-worker for their ability to quickly discern the root cause of a problem. While some people
are gifted with a natural talent for troubleshooting, it is a skill that can be learned like any other.
Sometimes the system to be analyzed is in so bad a state of affairs that there is no hope of ever getting it working
again. When investigators sift through the wreckage of a crashed airplane, or when a doctor performs an autopsy,
they must do their best to determine the cause of massive failure after the fact. Fortunately, the task of the
troubleshooter is usually not this grim. Typically, a misbehaving system is still functioning to some degree and
may be stimulated and adjusted by the troubleshooter as part of the diagnostic procedure. In this sense,
troubleshooting is a lot like scientific method: determining cause/effect relationships by means of live
experimentation.

Like science, troubleshooting is a mixture of standard procedure and personal creativity. There are certain
procedures employed as tools to discern cause(s) from effects, but they are impotent if not coupled with a
creative and inquisitive mind. In the course of troubleshooting, the troubleshooter may have to invent their own
specific technique -- adapted to the particular system they're working on -- and/or modify tools to perform a
special task. Creativity is necessary in examining a problem from different perspectives: learning to ask different
questions when the "standard" questions don't lead to fruitful answers.
If there is one personality trait I've seen positively associated with excellent troubleshooting more than any other,
its technical curiosity. People fascinated by learning how things work, and who aren't discouraged by a
challenging problem, tend to be better at troubleshooting than others. Richard Feynman, the late physicist who
taught at Caltech for many years, illustrates to me the ultimate troubleshooting personality. Reading any of his
(auto)biographical books is both educating and entertaining, and I recommend them to anyone seeking to develop
their own scientific reasoning/troubleshooting skills.

Questions to ask before proceeding:
 Has the system ever worked before? If yes, has anything happened to it since then that could cause the
problem?
 Has this system proven itself to be prone to certain types of failure?
 How urgent is the need for repair?
 What are the safety concerns, before I start troubleshooting?
 What are the process quality concerns, before I start troubleshooting (what can I do without causing
interruptions in production)?

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

These preliminary questions are not trivial. Indeed, they are essential to expedient and safe troubleshooting. They
are especially important when the system to be trouble-shot is large, dangerous, and/or expensive.
Sometimes the troubleshooter will be required to work on a system that is still in full operation (perhaps the
ultimate example of this is a doctor diagnosing a live patient). Once the cause or causes are determined to a high
degree of certainty, there is the step of corrective action. Correcting a system fault without significantly
interrupting the operation of the system can be very challenging, and it deserves thorough planning.
When there is high risk involved in taking corrective action, such as is the case with performing surgery on a
patient or making repairs to an operating process in a chemical plant, it is essential for the worker(s) to plan
ahead for possible trouble. One question to ask before proceeding with repairs is, "how and at what point(s) can I
abort the repairs if something goes wrong?" In risky situations, it is vital to have planned "escape routes" in your
corrective action, just in case things do not go as planned. A surgeon operating on a patient knows if there are
any "points of no return" in such a procedure, and stops to re-check the patient before proceeding past those
points. He or she also knows how to "back out" of a surgical procedure at those points if needed.

GENERAL TROUBLESHOOTING TIPS

When first a approaching a failed or misbehaving system, the new troubleshooter often doesn't know
where to begin. The following strategies are not exhaustive by any means, but provide the troubleshooter
with a simple checklist of questions to ask in order to start isolating the problem.

As tips, these troubleshooting suggestions are not comprehensive procedures: they serve as starting points only
for the troubleshooting process. An essential part of expedient troubleshooting is probability assessment, and
these tips help the troubleshooter determine which possible points of failure are more or less likely than others.
Final isolation of the system failure is usually determined through more specific techniques (outlined in the next
section -- Specific Troubleshooting Techniques).

PRIOR OCCURRENCE
If this device or process has been historically known to fail in a certain particular way, and the conditions leading
to this common failure have not changed, check for this "way" first. A corollary to this troubleshooting tip is the
directive to keep detailed records of failure. Ideally, a computer-based failure log is optimal, so that failures may
be referenced by and correlated to a number of factors such as time, date, and environmental conditions.

Example: The car's engine is overheating. The last two times this happened, the cause was low coolant level in
the radiator.
What to do: Check the coolant level first. Of course, past history by no means guarantees the present symptoms
are caused by the same problem, but since this is more likely, it makes sense to check this first.
If, however, the cause of routine failure in a system has been corrected (i.e. the leak causing low coolant level in
the past has been repaired), then this may not be a probable cause of trouble this time.

RECENT ALTERATIONS
If a system has been having problems immediately after some kind of maintenance or other change, the problems
might be linked to those changes.

Example: The mechanic recently tuned my car's engine, and now I hear a rattling noise that I didn't hear before I
took the car in for repair.
What to do: Check for something that may have been left loose by the mechanic after his or her tune-up work.

FUNCTION VS. NON-FUNCTION
If a system isn't producing the desired end result, look for what it is doing correctly; in other words, identify where
the problem is not, and focus your efforts elsewhere. Whatever components or subsystems necessary for the

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

properly working parts to function are probably okay. The degree of fault can often tell you what part of it is to
blame.

Example: The radio works fine on the AM band, but not on the FM band.
What to do: Eliminate from the list of possible causes, anything in the radio necessary for the AM band's function.
Whatever the source of the problem is, it is specific to the FM band and not to the AM band. This eliminates the
audio amplifier, speakers, fuse, power supply, and almost all external wiring. Being able to eliminate sections of
the system as possible failures reduces the scope of the problem and makes the rest of the troubleshooting
procedure more efficient.

HYPOTHESIZE
Based on your knowledge of how a system works, think of various kinds of failures that would cause this problem
(or these phenomena) to occur, and check for those failures (starting with the most likely based on circumstances,
history, or knowledge of component weaknesses).

Example: The car's engine is overheating.
What to do: Consider possible causes for overheating, based on what you know of engine operation. Either the
engine is generating too much heat, or not getting rid of the heat well enough (most likely the latter). Brainstorm
some possible causes: a loose fan belt, clogged radiator, bad water pump, low coolant level, etc. Investigate each
one of those possibilities before investigating alternatives.

LIKELY FAILURES IN PROVEN SYSTEMS

The following problems are arranged in order from most likely to least likely, top to bottom. This order has been
determined largely from personal experience troubleshooting electrical and electronic problems in automotive,
industry, and home applications. This order also assumes a circuit or system that has been proven to function as
designed and has failed after substantial operation time. Problems experienced in newly assembled circuits and
systems do not necessarily exhibit the same probabilities of occurrence.

OPERATOR ERROR
A frequent cause of system failure is error on the part of those human beings operating it. This cause of trouble is
placed at the top of the list, but of course the actual likelihood depends largely on the particular individuals
responsible for operation. When operator error is the cause of a failure, it is unlikely that it will be admitted prior to
investigation. I do not mean to suggest that operators are incompetent and irresponsible -- quite the contrary:
these people are often your best teachers for learning system function and obtaining a history of failure -- but the
reality of human error cannot be overlooked. A positive attitude coupled with good interpersonal skills on the part
of the troubleshooter goes a long way in troubleshooting when human error is the root cause of failure.

BAD WIRE CONNECTIONS
As incredible as this may sound to the new student of electronics, a high percentage of electrical and electronic
system problems are caused by a very simple source of trouble: poor (i.e. open or shorted) wire connections. This
is especially true when the environment is hostile, including such factors as high vibration and/or a corrosive
atmosphere. Connection points found in any variety of plug-and-socket connector, terminal strip, or splice are at
the greatest risk for failure. The category of "connections" also includes mechanical switch contacts, which can be
thought of as a high-cycle connector. Improper wire termination lugs (such as a compression-style connector
crimped on the end of a solid wire -- a definite faux pas) can cause high-resistance connections after a period of
trouble-free service.

It should be noted that connections in low-voltage systems tend to be far more troublesome than connections in
high-voltage systems. The main reason for this is the effect of arcing across a discontinuity (circuit break) in

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

higher-voltage systems tends to blast away insulating layers of dirt and corrosion, and may even weld the two
ends together if sustained long enough. Low-voltage systems tend not to generate such vigorous arcing across
the gap of a circuit break, and also tend to be more sensitive to additional resistance in the circuit. Mechanical
switch contacts used in low-voltage systems benefit from having the recommended minimum wetting current
conducted through them to promote a healthy amount of arcing upon opening, even if this level of current is not
necessary for the operation of other circuit components.
Although open failures tend to more common than shorted failures, "shorts" still constitute a substantial
percentage of wiring failure modes. Many shorts are caused by degradation of wire insulation. This, again, is
especially true when the environment is hostile, including such factors as high vibration, high heat, high humidity,
or high voltage. It is rare to find a mechanical switch contact that is failed shorted, except in the case of high-
current contacts where contact "welding" may occur in overcurrent conditions. Shorts may also be caused by
conductive buildup across terminal strip sections or the backs of printed circuit boards.

A common case of shorted wiring is the ground fault, where a conductor accidently makes contact with either
earth or chassis ground. This may change the voltage(s) present between other conductors in the circuit and
ground, thereby causing bizarre system malfunctions and/or personnel hazard.

POWER SUPPLY PROBLEMS
These generally consist of tripped overcurrent protection devices or damage due to overheating. Although power
supply circuitry is usually less complex than the circuitry being powered, and therefore should figure to be less
prone to failure on that basis alone, it generally handles more power than any other portion of the system and
therefore must deal with greater voltages and/or currents. Also, because of its relative design simplicity, a
system's power supply may not receive the engineering attention it deserves, most of the engineering focus
devoted to more glamorous parts of the system.

ACTIVE COMPONENTS
Active components (amplification devices) tend to fail with greater regularity than passive (non-amplifying)
devices, due to their greater complexity and tendency to amplify overvoltage/overcurrent conditions.
Semiconductor devices are notoriously prone to failure due to electrical transient (voltage/current surge)
overloading and thermal (heat) overloading. Electron tube devices are far more resistant to both of these failure
modes, but are generally more prone to mechanical failures due to their fragile construction.

PASSIVE COMPONENTS
Non-amplifying components are the most rugged of all, their relative simplicity granting them a statistical
advantage over active devices. The following list gives an approximate relation of failure probabilities (again, top
being the most likely and bottom being the least likely):

 Capacitors (shorted), especially electrolytic capacitors. The paste electrolyte tends to lose moisture with
age, leading to failure. Thin dielectric layers may be punctured by overvoltage transients.

 Diodes open (rectifying diodes) or shorted (Zener diodes).
 Inductor and transformer windings open or shorted to conductive core. Failures related to overheating

(insulation breakdown) are easily detected by smell.
 Resistors open, almost never shorted. Usually this is due to overcurrent heating, although it is less

frequently caused by overvoltage transient (arc-over) or physical damage (vibration or impact). Resistors
may also change resistance value if overheated!


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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

LIKELY FAILURES IN UNPROVEN SYSTEMS
"All men are liable to error;"
John Locke

Whereas the last section deals with component failures in systems that have been successfully operating for
some time, this section concentrates on the problems plaguing brand-new systems. In this case, failure modes
are generally not of the aging kind, but are related to mistakes in design and assembly caused by human beings.
WIRING PROBLEMS
In this case, bad connections are usually due to assembly error, such as connection to the wrong point or poor
connector fabrication. Shorted failures are also seen, but usually involve misconnections (conductors
inadvertently attached to grounding points) or wires pinched under box covers.
Another wiring-related problem seen in new systems is that of electrostatic or electromagnetic interference
between different circuits by way of close wiring proximity. This kind of problem is easily created by routing sets of
wires too close to each other (especially routing signal cables close to power conductors), and tends to be very
difficult to identify and locate with test equipment.

POWER SUPPLY PROBLEMS
Blown fuses and tripped circuit breakers are likely sources of trouble, especially if the project in question is an
addition to an already-functioning system. Loads may be larger than expected, resulting in overloading and
subsequent failure of power supplies.

DEFECTIVE COMPONENTS
In the case of a newly-assembled system, component fault probabilities are not as predictable as in the case of
an operating system that fails with age. Any type of component -- active or passive -- may be found defective or of
imprecise value "out of the box" with roughly equal probability, barring any specific sensitivities in shipping (i.e
fragile vacuum tubes or electrostatically sensitive semiconductor components). Moreover, these types of failures
are not always as easy to identify by sight or smell as an age- or transient-induced failure.

IMPROPER SYSTEM CONFIGURATION
Increasingly seen in large systems using microprocessor-based components, "programming" issues can still
plague non-microprocessor systems in the form of incorrect time-delay relay settings, limit switch calibrations, and
drum switch sequences. Complex components having configuration "jumpers" or switches to control behavior
may not be "programmed" properly.
Components may be used in a new system outside of their tolerable ranges. Resistors, for example, with too low
of power ratings, of too great of tolerance, may have been installed. Sensors, instruments, and controlling
mechanisms may be uncalibrated, or calibrated to the wrong ranges.

DESIGN ERROR
Perhaps the most difficult to pinpoint and the slowest to be recognized (especially by the chief designer) is the
problem of design error, where the system fails to function simply because it cannot function as designed. This
may be as trivial as the designer specifying the wrong components in a system, or as fundamental as a system
not working due to the designer's improper knowledge of physics.

I once saw a turbine control system installed that used a low-pressure switch on the lubrication oil tubing to shut
down the turbine if oil pressure dropped to an insufficient level. The oil pressure for lubrication was supplied by an
oil pump turned by the turbine. When installed, the turbine refused to start. Why? Because when it was stopped,
the oil pump was not turning, thus there was no oil pressure to lubricate the turbine. The low-oil-pressure switch
detected this condition and the control system maintained the turbine in shutdown mode, preventing it from
starting. This is a classic example of a design flaw, and it could only be corrected by a change in the system logic.

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

While most design flaws manifest themselves early in the operational life of the system, some remain hidden until
just the right conditions exist to trigger the fault. These types of flaws are the most difficult to uncover, as the
troubleshooter usually overlooks the possibility of design error due to the fact that the system is assumed to be
"proven." The example of the turbine lubrication system was a design flaw impossible to ignore on start-up. An
example of a "hidden" design flaw might be a faulty emergency coolant system for a machine, designed to remain
inactive until certain abnormal conditions are reached -- conditions which might never be experienced in the life of
the system.

POTENTIAL PITFALLS
Fallacious reasoning and poor interpersonal relations account for more failed or belabored troubleshooting efforts
than any other impediments. With this in mind, the aspiring troubleshooter needs to be familiar with a few
common troubleshooting mistakes.

Trusting that a brand-new component will always be good. While it is generally true that a new component
will be in good condition, it is not always true. It is also possible that a component has been mis-labeled and may
have the wrong value (usually this mis-labeling is a mistake made at the point of distribution or warehousing and
not at the manufacturer, but again, not always!).

Not periodically checking your test equipment. This is especially true with battery-powered meters, as weak
batteries may give spurious readings. When using meters to safety-check for dangerous voltage, remember to
test the meter on a known source of voltage both before and after checking the circuit to be serviced, to make
sure the meter is in proper operating condition.

Assuming there is only one failure to account for the problem. Single-failure system problems are ideal for
troubleshooting, but sometimes failures come in multiple numbers. In some instances, the failure of one
component may lead to a system condition that damages other components. Sometimes a component in marginal
condition goes undetected for a long time, then when another component fails the system suffers from problems
with both components.

Mistaking coincidence for causality. Just because two events occurred at nearly the same time does not
necessarily mean one event caused the other! They may be both consequences of a common cause, or they may
be totally unrelated! If possible, try to duplicate the same condition suspected to be the cause and see if the event
suspected to be the coincidence happens again. If not, then there is either no causal relationship as assumed.
This may mean there is no causal relationship between the two events whatsoever, or that there is a causal
relationship, but just not the one you expected.

Self-induced blindness. After a long effort at troubleshooting a difficult problem, you may become tired and
begin to overlook crucial clues to the problem. Take a break and let someone else look at it for a while. You will
be amazed at what a difference this can make. On the other hand, it is generally a bad idea to solicit help at the
start of the troubleshooting process. Effective troubleshooting involves complex, multi-level thinking, which is not
easily communicated with others. More often than not, "team troubleshooting" takes more time and causes more
frustration than doing it yourself. An exception to this rule is when the knowledge of the troubleshooters is
complementary: for example, a technician who knows electronics but not machine operation, teamed with an
operator who knows machine function but not electronics.

Failing to question the troubleshooting work of others on the same job. This may sound rather cynical and
misanthropic, but it is sound scientific practice. Because it is easy to overlook important details, troubleshooting
data received from another troubleshooter should be personally verified before proceeding. This is a common
situation when troubleshooters "change shifts" and a technician takes over for another technician who is leaving

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Information Sheet 5.1.1: General Principles in Troubleshooting Techniques

before the job is done. It is important to exchange information, but do not assume the prior technician checked
everything they said they did, or checked it perfectly. I've been hindered in my troubleshooting efforts on many
occasions by failing to verify what someone else told me they checked.

Being pressured to "hurry up." When an important system fails, there will be pressure from other people to fix
the problem as quickly as possible. As they say in business, "time is money." Having been on the receiving end of
this pressure many times, I can understand the need for expedience. However, in many cases there is a higher
priority: caution. If the system in question harbors great danger to life and limb, the pressure to "hurry up" may
result in injury or death. At the very least, hasty repairs may result in further damage when the system is
restarted. Most failures can be recovered or at least temporarily repaired in short time if approached intelligently.
Improper "fixes" resulting in haste often lead to damage that cannot be recovered in short time, if ever. If the
potential for greater harm is present, the troubleshooter needs to politely address the pressure received from
others, and maintain their perspective in the midst of chaos. Interpersonal skills are just as important in this realm
as technical ability!

Finger-pointing. It is all too easy to blame a problem on someone else, for reasons of ignorance, pride, laziness,
or some other unfortunate facet of human nature. When the responsibility for system maintenance is divided into
departments or work crews, troubleshooting efforts are often hindered by blame cast between groups. "It's a
mechanical problem . . . its an electrical problem . . . its an instrument problem . . ." ad infinitum, ad nauseum, is
all too common in the workplace. I have found that a positive attitude does more to quench the fires of blame than
anything else.

On one particular job, I was summoned to fix a problem in a hydraulic system assumed to be related to the
electronic metering and controls. My troubleshooting isolated the source of trouble to a faulty control valve, which
was the domain of the millwright (mechanical) crew. I knew that the millwright on shift was a contentious person,
so I expected trouble if I simply passed the problem on to his department. Instead, I politely explained to him and
his supervisor the nature of the problem as well as a brief synopsis of my reasoning, then proceeded to help him
replace the faulty valve, even though it wasn't "my" responsibility to do so. As a result, the problem was fixed very
quickly, and I gained the respect of the millwright.

Contributors
1. http://www.allaboutcircuits.com/vol_5/chpt_8/2.html
2. http://www.allaboutcircuits.com/vol_5/chpt_8/4.html

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Information Sheet 5.1.2: Specific Troubleshooting Techniques

Learning outcomes:
5 Troubleshooting techniques.
Learning Activity:
5.1 Familiarize some specific troubleshooting techniques.

Specific troubleshooting techniques
After applying some of the general troubleshooting tips to narrow the scope of a problem's location, there are techniques
useful in further isolating it. Here are a few:

Swap identical components
In a system with identical or parallel subsystems, swap components between those subsystems and see whether or not the
problem moves with the swapped component. If it does, you've just swapped the faulty component; if it doesn't, keep
searching!

This is a powerful troubleshooting method, because it gives you both a positive and a negative indication of the swapped
component's fault: when the bad part is exchanged between identical systems, the formerly broken subsystem will start
working again and the formerly good subsystem will fail.

I was once able to troubleshoot an elusive problem with carcass machine in a tire manufacturing company using this method:
in that section, Steelastic Department we happened to have a similar machine and same model. I swapped parts between the
electrical cabinets (magnetic relays, current transformers, electric solenoids -- one at a time) until the problem moved to the
other carcass machine. The problem happened to be a "weak" current transformer, and it only manifested itself under heavy
load. Normally, this type of problem could only be pinpointed using an oscilloscope. This technique, however, confirmed the
source of the problem with 100% accuracy, using no diagnostic equipment whatsoever.

Occasionally you may swap a component and find that the problem still exists, but has changed in some way. This tells you
that the components you just swapped are somehow different (different calibration, different function), and nothing more.
However, don't dismiss this information just because it doesn't lead you straight to the problem -- look for other changes in the
system as a whole as a result of the swap, and try to figure out what these changes tell you about the source of the problem.
An important caveat to this technique is the possibility of causing further damage. Suppose a component has failed because of
another, less conspicuous failure in the system. Swapping the failed component with a good component will cause the good
component to fail as well.

For example, suppose that a circuit develops a short, which "blows" the protective fuse for that circuit. The blown fuse is not
evident by inspection, and you don't have a meter to electrically test the fuse, so you decide to swap the suspect fuse with one
of the same rating from a working circuit. As a result of this, the good fuse that you move to the shorted circuit blows as well,
leaving you with two blown fuses and two non-working circuits. At least you know for certain that the original fuse was blown,
because the circuit it was moved to stopped working after the swap, but this knowledge was gained only through the loss of a
good fuse and the additional "down time" of the second circuit.

Another example to illustrate this caveat is the ignition system problem previously mentioned. Suppose that the "weak" ignition
coil had caused the engine to backfire, damaging the muffler. If swapping ignition system components with another vehicle
causes the problem to move to the other vehicle, damage may be done to the other vehicle's muffler as well. As a general rule,
the technique of swapping identical components should be used only when there is minimal chance of causing additional
damage. It is an excellent technique for isolating non-destructive problems.

Example 1: You're working on a CNC machine tool with X, Y, and Z-axis drives. The Y axis is not working, but the X and Z
axes are working. All three axes share identical components (feedback encoders, servo motor drives, servo motors).
What to do: Exchange these identical components, one at a time, Y axis and either one of the working axes (X or Z), and see
after each swap whether or not the problem has moved with the swap.

Example 2: A stereo system produces no sound on the left speaker, but the right speaker works just fine.
What to do: Try swapping respective components between the two channels and see if the problem changes sides, from left to
right. When it does, you've found the defective component. For instance, you could swap the speakers between channels: if
the problem moves to the other side (i.e. the same speaker that was dead before is still dead, now that its connected to the

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Information Sheet 5.1.2: Specific Troubleshooting Techniques

right channel cable) then you know that speaker is bad. If the problem stays on the same side (i.e. the speaker formerly silent
is now producing sound after having been moved to the other side of the room and connected to the other cable), then you
know the speakers are fine, and the problem must lie somewhere else (perhaps in the cable connecting the silent speaker to
the amplifier, or in the amplifier itself).

If the speakers have been verified as good, then you could check the cables using the same method. Swap the cables so that
each one now connects to the other channel of the amplifier and to the other speaker. Again, if the problem changes sides (i.e.
now the right speaker is now "dead" and the left speaker now produces sound), then the cable now connected to the right
speaker must be defective. If neither swap (the speakers nor the cables) causes the problem to change sides from left to right,
then the problem must lie within the amplifier (i.e. the left channel output must be "dead").

Remove parallel components
If a system is composed of several parallel or redundant components which can be removed without crippling the whole
system, start removing these components (one at a time) and see if things start to work again.

Example 1: A "star" topology communications network between several computers has failed. None of the computers are able
to communicate with each other.
What to do: Try unplugging the computers, one at a time from the network, and see if the network starts working again after
one of them is unplugged. If it does, then that last unplugged computer may be the one at fault (it may have been "jamming"
the network by constantly outputting data or noise).

Example 2: A household fuse keeps blowing (or the breaker keeps tripping open) after a short amount of time.
What to do: Unplug appliances from that circuit until the fuse or breaker quits interrupting the circuit. If you can eliminate the
problem by unplugging a single appliance, then that appliance might be defective. If you find that unplugging almost any
appliance solves the problem, then the circuit may simply be overloaded by too many appliances, neither of them defective.

Divide system into sections and test those sections
In a system with multiple sections or stages, carefully measure the variables going in and out of each stage until you find a
stage where things don't look right.

Example 1: A radio is not working (producing no sound at the speaker))
What to do: Divide the circuitry into stages: tuning stage, mixing stages, amplifier stage, all the way through to the speaker(s).
Measure signals at test points between these stages and tell whether or not a stage is working properly.

Example 2: An analog summer circuit is not functioning properly.

What to do: I would test the passive averager network (the three resistors at the lower-left corner of the schematic) to see that
the proper (averaged) voltage was seen at the non-inverting input of the op-amp. I would then measure the voltage at the
inverting input to see if it was the same as at the non-inverting input (or, alternatively, measure the voltage difference between
the two inputs of the op-amp, as it should be zero). Continue testing sections of the circuit (or just test points within the circuit)
to see if you measure the expected voltages and currents.

Simplify and rebuild
Closely related to the strategy of dividing a system into sections, this is actually a design and fabrication technique useful for
new circuits, machines, or systems. It's always easier begin the design and construction process in little steps, leading to
larger and larger steps, rather than to build the whole thing at once and try to troubleshoot it as a whole.
Suppose that someone were building a custom automobile. He or she would be foolish to bolt all the parts together without
checking and testing components and subsystems as they went along, expecting everything to work perfectly after its all
assembled. Ideally, the builder would check the proper operation of components along the way through the construction
process: start and tune the engine before its connected to the drivetrain, check for wiring problems before all the cover panels
are put in place, check the brake system in the driveway before taking it out on the road, etc.

Countless times I've witnessed students build a complex experimental circuit and have trouble getting it to work because they
didn't stop to check things along the way: test all resistors before plugging them into place, make sure the power supply is
regulating voltage adequately before trying to power anything with it, etc. It is human nature to rush to completion of a project,
thinking that such checks are a waste of valuable time. However, more time will be wasted in troubleshooting a malfunctioning
circuit than would be spent checking the operation of subsystems throughout the process of construction.

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Information Sheet 5.1.2: Specific Troubleshooting Techniques

Take the example of the analog summer circuit in the previous section for example: what if it wasn't working properly? How
would you simplify it and test it in stages? Well, you could reconnect the op-amp as a basic comparator and see if its
responsive to differential input voltages, and/or connect it as a voltage follower (buffer) and see if it outputs the same analog
voltage as what is input. If it doesn't perform these simple functions, it will never perform its function in the summer circuit! By
stripping away the complexity of the summer circuit, paring it down to an (almost) bare op-amp, you can test that component's
functionality and then build from there (add resistor feedback and check for voltage amplification, then add input resistors and
check for voltage summing), checking for expected results along the way.

Trap a signal
Set up instrumentation (such as a data-logger, chart recorder, or multimeter set on "record" mode) to monitor a signal over a
period of time. This is especially helpful when tracking down intermittent problems, which have a way of showing up the
moment you've turned your back and walked away.
This may be essential for proving what happens first in a fast-acting system. Many fast systems (especially shutdown "trip"
systems) have a "first out" monitoring capability to provide this kind of data.

Example #1: A turbine control system shuts automatically in response to an abnormal condition. By the time a technician
arrives at the scene to survey the turbine's condition, however, everything is in a "down" state and its impossible to tell what
signal or condition was responsible for the initial shutdown, as all operating parameters are now "abnormal."
What to do: One technician I knew used a videocamera to record the turbine control panel, so he could see what happened
(by indications on the gauges) first in an automatic-shutdown event. Simply by looking at the panel after the fact, there was no
way to tell which signal shut the turbine down, but the videotape playback would show what happened in sequence, down to a
frame-by-frame time resolution.

Example #2: An alarm system is falsely triggering, and you suspect it may be due to a specific wire connection going bad.
Unfortunately, the problem never manifests itself while you're watching it!
What to do: Many modern digital multimeters are equipped with "record" settings, whereby they can monitor a voltage, current,
or resistance over time and note whether that measurement deviates substantially from a regular value. This is an invaluable
tool for use in "intermittent" electronic system failures.

Contributors

1. http://www.allaboutcircuits.com/vol_5/chpt_8/2.html
2. http://www.allaboutcircuits.com/vol_5/chpt_8/4.html

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Job Sheet 5.1.3: Troubleshooting Techniques – Electrically Common Point

Learning outcomes:
5 Troubleshooting Techniques
Learning Activity:
5.1 Circuit Troubleshooting

Equipment / Resources:

 Terminal Block (4-points minimum), 2pcs.
 Dry Cell, 2pcs, 1.5 volts
 Switch, SPST
 VOM Tester
 Light Bulb, 3Vdc

Equipment / Resources:
At the end of these learning activities you should be able to practice some trouble-shooting techniques and arrive
to conclusions in determining sources of faults and causes in a simple circuitry.

Problem #1: “ELECTRICALLY COMMON" POINT
In this battery-switch-lamp circuit, the metal filament wire inside the lamp has burned up, so that it no longer forms
an electrically continuous connection. In other words, the filament has failed open."

Of course, this means the lamp will not turn on, no matter what is done with the switch. It also means that most of
the voltage measurements taken in the circuit will be the same as with a properly operating circuit. There is,
however, one voltage measurement which will be different in the circuit with the burned-out filament than in a
properly working circuit. Identify what pair or pairs of terminal block points this different voltage will be measured
between, what switch state (ON or OFF) it will appear in, and what this different voltage measurement will actually
be relative to the battery voltage.

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Job Sheet 5.1.3: Troubleshooting Techniques – Electrically Common Point

Problem #2: “ELECTRICALLY COMMON" POINT
Suppose a technician were troubleshooting the following circuit, whose light bulb refused to light up:

Instruction:

1. It is NOT necessary to construct the circuit as shown above, your imagination suffices.
2. Record the data on a piece of paper divided into two columns: Observations, and Conclusions, drawing

a horizontal line underneath each conclusion after it is made:
3. Columns A are the listed scenarios.
4. Column B is where you write your possible conclusion/s.

OBSERVATION CONCLUSIONS
(What I measured, sensed or did) (What I think)

Turned switch ON –no light

Measured 12 volts AC between
terminals TB1-1 and TB2-1

Measured NO VOLTAGE across the
light bulb (between TB2-2 and TB2-3

Measured NO VOLTAGE across switch
(between TB1-1 and TB1-3

Measured 12 volts AC between
terminals TB2-1 and TB2-3

Measured 12 volts AC between
terminals TB1-3 and TB2-1

Measured 12 volts AC between
terminals TB2-1 and TB2-2

Replace wire between TB2-1 and TB2-2
and the light bulb now lights up!

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Work sheet 5.1.4: Troubleshooting Techniques – Electrically Common Point

Learning outcomes:
5 Troubleshooting Techniques
Learning Activity:
5.1 Troubleshooting Techniques

1. Determine if the light bulb will de-energize for each of the following breaks in the circuit. Consider
just one break at a time:

Figure 1: Wire Loop
Choose one option for each point:

A: de-energize / no effect
B: de-energize / no effect
C: de-energize / no effect
D: de-energize / no effect
E: de-energize / no effect
F: de-energize / no effect

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Work sheet 5.1.4: Troubleshooting Techniques – Electrically Common Point

2. Examine the following illustration of a simple battery-switch-lamp circuit, connected together using
screw-terminal blocks, each connection point on each terminal block identified by a unique number:

Determine state whether or not voltage should be present between the following pairs of terminal block
points with the switch in the ON position:

TERMINAL SWITCH IS SWITCH IS
COMBINATION TURNED ON TURNED OFF

Points 1 and 5: Presence of Voltage Presence of Voltage
Points 6 and 7:
Points 4 and 10: YES NONE YES NONE
Points 9 and 12:
Points 6 and 12:
Points 9 and 10:
Points 4 and 7:

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Information Sheet 6.1.1: Synopsis of Sensors

Learning outcomes:
6 Repair Mechatronics Devices and Systems.
Learning Activity:
6.1 Factors to consider in Repair/Replacement of Mechatronics Devices and Systems.

1 INTRODUCTION

Detection: A vital function
The detection function is vital because it is the first link in the chain of information (see Fig. 1) for an industrial
process. In an automatic system, detectors collect information about:

 All the events that are needed to control it, so that they can be taken into account by the control systems,
using an established program

 The progress of the various stages of the process when this program is executed

1.2 The various detection functions
Detection requirements are extremely varied. The most basic needs are as follows:

 Monitoring the presence, absence or position of an object
 Verifying the passing, travel or obstruction of objects
 Counting

These requirements are generally met using “discrete” devices, as in typical applications for detecting parts in
production lines or handling activities, as well as for detecting people and vehicles.

There are other, more specific requirements, such as the detection of:
 Presence (or level) of gas or liquid
 Shape
 Position (angular, linear)
 Tags, with reading and writing of coded information

In addition to these, there are numerous requirements concerning the environment especially; depending on their
location, detectors have to be resistant to:

 Moisture or immersion (e.g. watertight reinforced seal)
 Corrosion (chemical industries or even food and beverage installations)

 Extreme temperature fluctuations (e.g. tropical regions)

 All types of dirt (outside or inside machinery)
 And even vandalism…

In order to meet all these requirements, manufacturers have designed all sorts of detectors using various
technologies.

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Information Sheet 6.1.1: Synopsis of Sensors

1.3 The various detector technologies
Detector manufacturers utilize a number of different physical measurement principles, the most important being:

 Mechanical (pressure, force) for electromechanical limit switches
 Electromagnetism (field, force) for magnetic sensors, inductive proximity sensors
 Light (power or deflection) for photoelectric cells
 Capacitance for capacitive proximity sensors
 Acoustic (wave travel time) for ultrasonic detectors
 Fluid (pressure) for pressure switches
 Optical (image analysis) for vision

These principles offer advantages and limitations for each type of sensor: for example, some are rugged but have
to be in contact with the part being detected; others can be located in aggressive environments but can only be
used with metal parts. The aim of the description of these various technologies in the following sections is to
explain the installation and operating requirements for the sensors available on the market in the automation and
industrial devices sector.

1.4 Auxiliary detector functions

Various functions have been developed to make detectors easier to use, self-teach mode being one.

With this teach function, the effective detection range of the device can be defined simply by pressing a button: for

example, learning the ultra- minimum and maximum ranges

(suppression of foreground and background), and environment recognition for photoelectric detectors.

2 ELECTROMECHANICAL LIMIT SWITCHES
Detection is achieved by means of physical contact (feeler or actuator) with an object or moving part. The
information is sent to the processing system via an electrical contact (discrete).

These devices (actuator and electrical contact) are known as limit switches. They are used in all automated
systems and in a wide range of applications because of the many inherent advantages in their technology.

2.1 Detection movements
A feeler or actuator may move in various ways (see Fig. 2), allowing it to detect in multiple positions and adapt
easily to the objects to be detected:

 Rectilinear
 Angular
 Multi-directional

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Information Sheet 6.1.1: Synopsis of Sensors

2.2 Contact operating mode
The products available from manufacturers are characterized by the technology used to move the contacts.
Snap-action contact
The movement of the contacts is characterized by the phenomenon of hysteresis, in other words, by distinctly
different tripping and reset points (see Fig. 3 opposite page).
The speed at which the moving contacts move is independent of the actuator speed. This feature means that
satisfactory electrical performance can be obtained even at low actuator speeds. Increasingly, limit switches with
snap-action contacts have contacts with a positive opening action: this relates to the NC contact and is defined as
follows:
“A device meets this requirement when all its NC contact elements can be moved with certainty to their open
position, in other words, with no flexible link between the moving contacts and the actuator to which the operating
force is applied.” This relates to the electrical contact on the limit switch (see Fig. 3) but also to the actuator, which
has to transmit the movement without deformation. The use of positive opening action devices is mandatory in
safety applications.

Slow-action contact, also known as slow break (see Fig. 4 )
This operating mode is characterized by:

 Identical tripping and reset points
 Moving contact travel speed equal or proportional to the actuator speed (which must not be less than 0.1

m/s = 6 m/min). Below these values, the contacts open too slowly, which is detrimental to the correct
electrical operation of the contact (risk of arc being maintained for too long).
 The opening distance also depends on the actuator travel.
The design of these contacts means that they are inherently positive opening: the plunger acts directly on the
moving contacts.

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Information Sheet 6.1.1: Synopsis of Sensors

3 INDUCTIVE PROXIMITY SENSORS
Due to their physical operating principle, these sensors only work on metallic materials.
3.1 Principle
An inductive circuit (induction coil L) is the sensitive element. This circuit is connected to a capacitor with
capacitance C to form a resonant circuit with a frequency Fo, which is generally between 100 kHz and 1 MHz.
An electronic circuit is used to maintain the system oscillations in accordance with the formula below:

These oscillations generate an alternating magnetic field in front of the coil. A metal screen positioned in the field
emits eddy currents, which induce an additional charge, thereby modifying the oscillation conditions (see Fig. 5 ).
The presence of a metal object in front of the sensor reduces the quality factor of the resonant circuit.
Case 1, without metal screen:

Case 2, with metal screen:

Detection is achieved by measuring the variation in the quality factor (from 3% to around 20% at the detection
threshold)
The approach of the metal screen results in a reduction in the quality factor and hence a reduction in the
amplitude of the oscillations. The sensing distance depends on the nature of the metal being detected (its

3.2 Description of an inductive sensor (see Fig. 6a)
Transducer: This comprises a multifilament copper wire (Litz wire) coil positioned inside a half ferrite pot which
directs the field lines towards the front of the sensor.
Oscillator: There are many different types of oscillator available, including oscillators with a fixed negative
resistance -R, which is equal in absolute value to the parallel resistance Rp of the oscillating circuit at the nominal
range (see preceding section). => If the object to be detected is beyond the nominal range, |Rp| > |-R| so
oscillation is maintained. => Conversely, if the object to be detected is inside the nominal range, |Rp| < |-R| so
oscillation is not maintained and the oscillator is blocked.
Shaping stage: This comprises a peak detector followed by a comparator with two thresholds (trigger) to prevent
untimely switching when the object to be detected is close to the nominal range. It creates what is known as the
sensor hysteresis (see Fig. 6b opposite page).
Supply and output stages: The one allows the sensor to be powered across a broad supply voltage range (from
10 V DC to 264 V AC). The other, the output stage, controls loads from 0.2 A DC to 0.5 A AC, with or without
short circuit protection.

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Information Sheet 6.1.1: Synopsis of Sensors

3.3 Influence quantities in inductive sensing
Certain characteristics particularly affect inductive sensing devices, notably:

 Sensing distance. This depends on the size of the sensing area. Sn: Nominal range (on mild steel) varies
from 0.8 mm (sensor diameter 4) to 60 mm (sensor 80 x 80).

 Hysteresis: Differential travel (from 2 to 10% of Sn), which prevents bouncing on switching
 Frequency of passage of objects in front of the sensor, known as the switching frequency (maximum

current 5 kHz).

3.4 Specific functions
 Sensors protected against magnetic fields generated by welding machines
 Analog output sensors
 Sensors with a correction factor of 1, where the sensing distance is independent of whether the metal
being detected is ferrous or nonferrous (see Fig. 7 )
 Selective sensors for ferrous and non-ferrous materials
 Rotation control sensors: These under speed sensors are sensitive to the frequency of passage of metal
objects.
 Sensors for explosive atmospheres (NAMUR standards)

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Information Sheet 6.1.1: Synopsis of Sensors

4 CAPACITIVE PROXIMITY SENSORS
This technology can be used to detect all types of conductive and insulating materials, such as glass, oil, wood
and plastics.
4.1 Principle
The sensing face of the sensor constitutes the armature of a capacitor.
A sine-wave voltage is applied to this face, creating an alternating electrical field in front of the sensor. Since this
sine-wave voltage is referenced in relation to a reference potential (ground or machine ground, for example), the
second armature consists of an electrode connected to this reference potential (machine frame, for example).
These two electrodes facing each other form a capacitor of capacitance:

Case 1: No object between the 2 electrodes (see Fig. 8 )

Case 2: Insulating object between the 2 electrodes (see Fig. 9 )

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Information Sheet 6.1.1: Synopsis of Sensors

In this case the ground electrode can be the metal belt of a conveyor, for example.
the value of C allows the presence of the insulating object to be detected.
Case 3: Conductive object between the 2 electrodes (see Fig. 10 )

The presence of a metal object thus leads to a rise in the value of C.

4.2 The various types of capacitive sensor

Capacitive sensors without a ground electrode
These sensors use the principle described above.
A path to ground (reference potential) is needed in order to detect an object. They are used for detecting
conductive materials (metal, water) at considerable distances. Typical application: Detection of conductive
materials through an insulating material (see Fig. 11).

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Information Sheet 6.1.1: Synopsis of Sensors

Capacitive sensors with a ground electrode
It is not always possible to find a path to ground, as would be the case if we wanted to detect the insulating
container in the previous example. The solution, therefore, is to incorporate the ground electrode on the sensing
face.

This creates an electrical field, which is independent from a path to ground (see Fig. 12 ).

Application: Detection of all materials. Possibility of detecting insulating or conductive materials behind an
insulating partition, e.g. cereals in a cardboard box.

4.3 Influence quantities for a capacitive sensor
The sensitivity of capacitive sensors according to the basic equation cited above (section 4.1) depends on both
the distance between the object and the sensor and the material from which the object is made.

 Sensing distance

object is made. To enable them to detect a wide variety of materials, capacitive sensors are generally
equipped with a potentiometer, which allows their sensitivity to be adjusted.

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Information Sheet 6.1.1: Synopsis of Sensors

 Material
The table in Figure 13 gives the dielectric constants of a number of materials.

5 PHOTOELECTRIC SENSORS
The operating principle of these sensors allows them to detect all types of object, including opaque, reflective and
even almost transparent objects. They are also used for detecting people (automatic doors, security barriers).
5.1 Principle (see fig. 14)
A light-emitting diode (LED) emits pulses of light, generally in the near infrared range (850 to 950 nm). This light
is received or not received by a photodiode or phototransistor, depending on whether an object to be detected is
present. The photoelectric current generated is amplified and compared with a reference threshold to provide a
discrete signal.

5.2 The various detection systems
Thru-beam (see Fig. 15)
The emitter and receiver are contained in separate housings. The emitter: a LED positioned at the focal point of a
focusing lens, creates a parallel light beam. The receiver: a photodiode (or phototransistor) positioned at the focal
point of a focusing lens, supplies a current, which is proportional to the energy received.

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The system supplies a discrete signal according to the presence or absence of the object in the beam.
 Strength: The sensing distance (range) can be long (up to 50 m or more); it depends on the size of the
lenses and therefore of the sensor.
 Weaknesses: The need for 2 housings, hence 2 separate power supplies, and for sensing distances of
more than 10 m alignment can also be difficult.

Reflex systems
There are actually two types of “reflex” system: standard reflex and polarized reflex.

Reflex (see Fig. 16)
The light beam is generally in the near infrared range (850 to 950 nm).

 Strengths: The emitter and receiver are in the same housing (only one supply cable). The sensing
distance (range) is still long, although shorter than that for thru-beam systems (up to 20 m).

 Weakness: A reflective object (window, car body, etc.) may be interpreted as a reflector and not detected.

The diagrams representing the reflex photoelectric detection systems presented in this section are intended
purely as an aid to understanding the devices used. They are not an accurate optical representation, as the
distance between the object and the detector is far greater than the gap between the emitter and the receiver; the
emitted and received rays can thus be considered to be parallel.

Polarized reflex (see Fig. 17)
The light beam used is generally in the red range (660 nm). The emitted radiation is polarized vertically by a linear
polarizing filter. The reflector changes the polarization state of the light, so part of the radiation returned has a
horizontal component.
The receiving linear polarizing filter allows this component to pass through and the light reaches the receiver.

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Information Sheet 6.1.1: Synopsis of Sensors

 Unlike the reflector, a reflective object (mirror, sheet metal, window) does not change the polarization
state. The light
reflected by the object is therefore unable to reach the receiving polarizer (see Fig. 18 next page).

 Strength: This type of sensor overcomes the weakness of standard reflex detection.
 Weaknesses: However, it is more expensive and the sensing distances are shorter:

IR reflex —> 15 m
Polarized reflex —> 8 m

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Information Sheet 6.1.1: Synopsis of Sensors

Diffuse system (on object)
 Standard diffuse (see Fig. 19 next page) This system utilizes the direct reflection (diffuse) from the object
to be detected.

 Strength: No reflector is needed.
 Weaknesses: The sensing distance for this system is very short (up to 2 m). It also varies according to

the color of the object to “see” and the background behind it (at a given setting, the sensing distance is
longer for a white object than for a gray or black object), and a background, which is lighter than the
object to be detected can make detection impossible.
 Diffuse with background suppression (see Fig. 20
This detection system uses triangulation. The sensing distance (up to 2 m) does not depend on the reflectivity of
the object, only on its position: a light object is detected at the same distance as a dark one. In addition, any
background beyond the sensing zone is ignored.

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Information Sheet 6.1.1: Synopsis of Sensors

OPTICAL FIBERS
Principle
A reminder of the principle can be found in Figure 21. There are different types of optical fiber: multimode and
single-mode (see Fig. 22 ).

The propagation of light waves in an optical fiber is based on total internal reflection.
Total internal reflection occurs when a light ray passes from one medium to another, which has a lower refractive
index. Furthermore, light is completely reflected with no loss of light when the angle of incidence of the light ray is

Total internal reflection is governed by two factors: the refractive indexes of the two media and the critical angle.

These factors are linked by the following equation:

If we know the refractive indexes of the two interface materials, the critical angle is simple to calculate.
Physics defines the refractive index of a substance as the relation between the speed of light in a vacuum (c) and
its speed in the material (v).

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Information Sheet 6.1.1: Synopsis of Sensors

c Multimode fibers
These are fibers in which the central core, which conducts the light, has a large diameter in comparison to the
wavelength used

Two types of propagation are used in these fibers: step-index or graded-index.

 Single-mode
By contrast, these fibers have a very small diameter in comparison to the wavelength used

They use step-index propagation. These fibers are mainly used in telecommunications. This brief reminder
illustrates the care that has to be taken when using these fibers, in terms of pulling them, for example (reduced
tensile strength and moderate radii of curvature, according to manufacturers’ specifications). Multimode optical
fibers are the most widely used in industry, as they offer the advantages of electromagnetic ruggedness (EMC –
electromagnetic compatibility) and ease of use.

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Information Sheet 6.1.1: Synopsis of Sensors

 Sensor technology
The optical fibers are positioned in front of the emitting LED and in front of the receiving photodiode or
phototransistor (see Fig. 23).

This principle allows:
 Positioning of electronic components away from the monitoring point
 Use in confined areas or at high temperature
 Detection of very small objects (mm range)
 Depending on the configuration of the fiber ends, operation in thru-beam or proximity mode

Note that the connections between the emitting LED or the receiving phototransistor and the optical fiber must be
made with extreme care to minimize light signal losses.

5.3 Influence quantities in detection using photoelectric systems
A number of factors can influence the performance of these detection systems.

Some have been mentioned already:
 Distance (sensor-object)
 Type of object to be detected (diffusing, reflective or transparent material, color, and size)
 Environment (ambient light, background, etc.)

Contributors
1. http://www.infrainternational.com/downloads/specifications/General_Specifications_2009.pdf
2. Cahier Technique Schneider Electric
3.

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Information Sheet 6.1.2: Sensors Applications

Learning outcomes:
6 Repair Mechatronics Devices and Systems.
Learning Activity:
6.1 Familiarize some application of sensors

Sensor Applications

There are any number of applications where sensors can be utilized, and as you have seen throughout this
information sheet there are a number of sensors to chose from. Choosing the right sensor can be confusing and
takes careful thought and planning. Often, more than one sensor will do the job. As the application becomes more
complex the more difficult it is to choose the right sensor for a given application. The following application guide
will help you find the right sensor for the right application.

Code No. MAINTAIN AND REPAIR MECHATRONIC Date: Developed Date: Revised Page #
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Information Sheet 6.1.2: Sensors Applications

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Information Sheet 6.1.2: Sensors Applications

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Information Sheet 6.1.2: Sensors Applications

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Information Sheet 6.1.2: Sensors Applications

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Information Sheet 6.1.2: Sensors Applications

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Information Sheet 6.1.2: Sensors Applications

Application Inquiry

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Information Sheet 6.1.2: Sensors Applications

Providing a sensing device solution requires both knowledge of the application and answers to specific questions
to obtain key additional facts. This page is intended to be photocopied and used as a self-help guide in assessing
the scope of sensor applications. The information recorded on this form may then be cross-checked with the
product specifications found in our “BERO - Sensing Solutions” catalog to obtain a potential solution to your
application. If your application involves machine guard safety interlocking, the use of standard position sensors
could result in serious injury or death. Please contact SE&A Sensor Marketing for assistance at
(630) 879-6000.

Contributors

1. http://www.allaboutcircuits.com/vol_5/chpt_8/2.html
2. http://www.allaboutcircuits.com/vol_5/chpt_8/4.html

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Operation Sheet 6.1.3: Guide for Sensor Installation: Photoelectric Sensors

Learning outcomes:
6 Maintain Mechatronics devices and systems
Learning Activity:
6.1 Guidelines in installing a Photoelectric sensor.

INSTRUCTIONS FOR CORRECT INSTALLATION

THESE PHOTOELECTRIC SENSORS ARE NOT SAFETY DEVICES, THEREFORE THEY
CANNOT BE USED TO PREVENT INJURIES TO PERSONS, DAMAGES, INDUSTRIAL
DAMAGES, ACCIDENTS.

CONNECTIONS:
1) Do not exceed the voltage limits printed on the product label. For DC photoelectric sensors use stable
tension.
2) Do not connect the photoelectric sensors power supply cables down-steam from other devices and make
sure that they are directly connected to the mains.
3) If the power supply source is a switching voltage regulator, connect the FG (Frame Ground) terminal to
the ground.
4) Connect to ground the FG (Frame Ground) terminal and all metallic parts of every industrial machinery or
not if a photoelectric sensor is used in it.
5) Do not use the photoelectric sensor near electromagnetic or high frequency fields.
6) The cables of photoelectric sensors must be separate from the power supply cables, from the engines
cables, from the inverters cables, or from any other electromagnetic device because induction noise could
cause malfunction or damage to the photoelectric sensors. Separate the wires of the photoelectric
sensors from the above indicated cables and then insert the wires into an earthed metal conduit.
7) After making all operations mentioned in the above point 6, if inductive interference exists, an adequate
transient suppression filter must be used on the power supply line in proximity to the photoelectric
sensors.
8) When a large distance by the connection wires to the sensor has to be covered, use conductors with a
cross-section of a least 0.50 mm2 and do not exceed the maximum distance of 100 m.
9) The output signal of a photoelectric sensors cannot be used during the start up delay.
10) Several sensors should not be connected in series, whereas several sensors can be connected in
parallel.

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Operation Sheet 6.1.3: Guide for Sensor Installation: Photoelectric Sensors

ASSEMBLY:
1) For correct assembly and alignment, all the accessories supplied with the sensor must be used.
2) To regulate the sensitivity adjustment trimmer use a suitable srew-driver without exerting excessive force.
3) Do not turn too much fixing screws or nuts to avoid electrical or mechanical damages.
4) Mounting photoelectric sensors side by side, leave an appropriate place between them to avoid mutual
interference.
5) When installing two or more emitters and the receivers side by side, alternate the emitter with the receiver
or install a light barrier to prevent reciprocal interferences. Avoid reflection coming from the side or back
walls or objects.
6) Do not expose the photoelectric sensors to direct source of fluorescent light which could prevent the
correct working. Do not exceed the immunity limits to external light.
7) Do not use organic solvents or corrosive liquids to clean the lenses of the photo-electric sensors. The
optical parts must be cleaned with a soft cloth and then dried.
8) Do not use the sensors in open air without adequate protection.
9) Do not use the photoelectric sensors in dusty places, in presence of steam, gases, corrosive steams,
corrosive liquids, rain or water jets. Do not let condensation form on the sensor lenses.
10) Do not exceed the indicate temperature limits.
11) Do not subject the appliance to strong vibrations or to shocks which can damage the sensor or can harm
its impermeability.
12) Although some ranges of photoelectric sensors are protect IP 67, this does not mean that these devices
can be used to detect objects in water or in the rain.

SETTING OF NON-ADJUSTABLE PHOTOELECTRIC SENSORS

DIFFUSE REFLECTIVE
1) Mount the photoelectric sensor in working position but do not fasten it completely.
2) Supply power to the sensor.
3) Position the object to be detected, making sure that the optical axis is perpendicular to the surface of the
object. If the surface to be detected is shiny, incline the optical axis by a few degrees so that the specular
reflection is blocked out.
4) Set up the photoelectric sensor in the worst working conditions:
 smaller object to be detected;
 darker object or part of object;
 object in the furthest possible position in relation to the photoelectric sensor;
5) If the state LED indicator is off, move the photoelectric sensor towards the object to be detected until the
LED lights up. If the LED is already illuminated, move the photoelectric sensor away until the state LED
goes off and then move it nearer again until when it re-lights up (position A).
6) If there is no background go to point 6.1. If there is background go to point 6.2.
6.1) NO BACKGROUND: move the photoelectric sensor nearer to the object by a distance of 15% of the
detection distance.

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Operation Sheet 6.1.3: Guide for Sensor Installation: Photoelectric Sensors

6.2) BACKGROUND PRESENT: remove the object to be detected (the LED will go off, if it does not go
off, proceed to point 6.3) and move the photoelectric sensor towards the background until the state LED
lights up (position B). Position the photoelectric sensor at a distance between position A (determined in
point 5) and position B where the LED goes off.
6.3) If the photoelectric sensor still detects the background, one solution may be to incline the optical
detection axis in relation to the normal of the plane of the background by about 10° and repeat the setting
procedure from point 4 onwards. If the LED still does not go off with this procedure, a model of
photoelectric sensor with a more restricted range will have to be chosen.
7) The system should then be securely fixed in place.

RETRO REFLECTIVE - POLARIZED RETRO REFLECTIVE
1) Fit the photoelectric sensor and the reflector facing each other within the operating range.
2) Supply power to the sensor.
3) Carefully align the photoelectric sensor and reflector unit around the optical axis in order to set limits of
the operation area and position the photoelectric sensor approximately at the centre.
4) Make sure that when an object is placed between the photoeletric sensor and the reflector, the state LED
indicator lights up.
5) The photoelectric sensor should switch when an obstacle, placed in proximity to the retroreflective,
obscures at least 30/40% of its surface. If switching occurs with less darkness, align the photoelectric
sensor and the retroreflective better so that the above condition is achieved.
6) The system should then be securely fixed in place.

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Operation Sheet 6.1.3: Guide for Sensor Installation: Photoelectric Sensors

DETECTION OF REFLECTING OBJECTS
When the object to be detected is particularly reflective, polarized retroreflective sensors should be used.
In any case, the photoelectric sensor should be orientated as in the diagram in order to avoid false reflections
given by the object.

N. B.: The reflex and polarized reflex photoelectric sensors should never be used for maximum range values in
the presence of adverse environmental conditions (such as dust, smoke, etc.) which could reduce the efficiency of
the sensors.

EMITTER - RECEIVER THRU-BEAM
1) Fit the emitter and the receiver facing each other within the indica-ted operating range.
2) Supply power to the two photoelectric sensors.
3) Align the emitter and receiver carefully: orientate the receiver around the optical axis in order to set the
limits of the operation area and position the receiver approximately at the centre.
4) Make sure that when an object is placed between the emitter and receiver, the state LED indicator lights
up.
5) The photoelectric sensor should switch when an obstacle, placed in proximity to the receiver, obscures at
least 30/40% of its surface. If switching occurs with less darkness, align the emitter and the receiver
better so that the above condition is achieved.
6) The system should then be securely fixed in place.

N. B.: The emitter and receiver barriers should never be used for maximum
range values in the presence of adverse environmental conditions (such as
dust, smoke, etc.) which could reduce the efficiency of the sensors.

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DEVICES AND SYSTEMS Oct 28, 2010

Job Sheet 6.1.4: Repair Mechatronics Devices and Systems – Adjusting Photoelectric
Sensor

Learning outcomes:
6 Repair Mechatronics Devices and Systems
Learning Activity:
6.1 Adjusting Photoelectric Sensor

Equipment / Resources:

 Diffuse reflective Sensor
 Retro reflective - Polarized retro reflective Sensor
 Emitter - Receiver Thru-beam
 Optical brackets
 Flat Screwdriver, 4mm
 Wooden block
 Disc Reflector
 Power Suppy 220/12-0-12 Vac

At the end of these learning activities you should be able to adjust a photoelectric sensor according to its desired
working operation

DIFFUSE REFLECTIVE AND BACKGROUND SUPPRESSION
1) Mount the photoelectric sensor in working position but do not fasten it completely.
2) Supply power to the sensor.
3) Position the object to be detected; making sure that the optical axis is perpendicular to the surface of the
object. If the surface to be detected is shiny, incline the optical axis by a few degrees so that the specular
reflection is blocked out.
4) Set up the photoelectric sensor in the worst working conditions:
 smaller object to be detected;
 darker object or part of object;
 object in the furthest possible position in relation to the photoelectric sensor;
5) Turn the sensitivity adjustment trimmer clockwise (+) until maximum sensitivity is reached: the yellow LED
should be illuminated; if this is not the case adjust orientation and/or bring the photoelectric sensor
nearer.
6) Turn the adjustment trimmer anticlockwise (-) until the LED goes out.
7) Turn the adjustment trimmer clockwise (+) until the LED lights up again (hysteresis recovery); this
determines point A.

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Job Sheet 6.1.4: Repair Mechatronics Devices and Systems – Adjusting Photoelectric
Sensor

8) If there is no background go to point 8.1. If there is background go to point 8.2.
- 8.1) NO BACKGROUND: turn the trimmer to a position between point A and the extreme clockwise

position (determined in point 5).
- 8.2) BACKGROUND PRESENT: remove the object to be detected (the LED will go out: if it does not go

out proceed to point 8.3) turn the trimmer clockwise until the state LED lights up (point B). Turn the
trimmer to a position between point A and point B where the LED goes out.
- 8.3) If the photoelectric sensor still detects the background, one solution may be to incline the optical
detection axis in relation to the normal of the plane of the background by about 10° and repeat the
adjustment procedure from point 5 onwards. If, with this procedure, the LED still does not go off in the
presence of background, the photoelectric sensor should be moved nearer the object to be detected and
the adjustment procedure from point 5 onward should be repeated.
9) The system should then be securely fixed in place.

Target position for background suppression
Mount the sensor according to the two allowed movement directions of the target:

If the target is specular (such as an aluminum or a copper foil) or if its surface is glossy, the sensor may not work
correctly because of the reflections.

 When there is a specular or a glossy surface object behind the target, a little angular change of
background object may cause an erroneous activation of the sensor. In that case, re-install the sensor
tilted to verify the detection once again.

 Tilt the sensor slightly upwards in order to prevent an irregular reflection where the sensor is placed on a
specular surface or substance.

Code No. MAINTAIN AND REPAIR MECHATRONIC Date: Developed Date: Revised Page #
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Job Sheet 6.1.4: Repair Mechatronics Devices and Systems – Adjusting Photoelectric
Sensor

RETRO REFLECTIVE - POLARIZED RETRO REFLECTIVE
1) Fit the photoelectric sensor and the reflector facing each other within the operating range
2) Supply power to the sensor.
3) Make sure that the sensitivity adjustment trimmer is in the extreme clockwise position (+) and carefully
align the photoelectric sensor and reflector around the optical axis in order to set the limits of the
operation area and position the photoelectric sensor approximately at the centre until the LED goes out.

4) Slowly turn the adjustment trimmer anticlockwise (-) until the LED lights up and then improve orientation
so that the LED goes off. Once better orientation is achieved, turn the trimmer clockwise (+) until the
extreme clockwise position.

5) Position the object to be detected between the photo-electric sensor and the reflector and check that the
yellow LED is illuminated, if the yellow LED is off, turn the trimmer anticlockwise (-) until the yellow LED
lights up: point A.

6) Remove the object and gradually turn the trimmer anticlockwise (-) until the yellow LED lights up: point B.
7) Position the adjustment trimmer half way between point A and point B in order to achieve the ideal

position.
8) The system should then be securely fixed in place.

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Job Sheet 6.1.4: Repair Mechatronics Devices and Systems – Adjusting Photoelectric
Sensor

DETECTION OF REFLECTING OBJECTS

When the object to be detected is particularly reflective, polarized retroreflective sensors should be used.
In any case, the photoelectric sensor should be orientated as in the diagram in order to avoid false reflections
given by the object.

N. B.: The adjustment obtained in point 7 is the most efficient for shiny and/or semi-transparent objects; if the
objects to be detected are opaque and nonreflecting, the trimmer can be brought to the extreme clockwise
position which will allow the photoelectric sensor to operate even in very dusty environments.

EMITTER - RECEIVER THRU-BEAM
1) Fit the emitter and the receiver facing each other within the indicated operating range.
2) Supply power to the two photoelectric sensors.
3) Make sure that the sensitivity adjustment trimmer of the receiver is in the extreme clockwise position (+)
and carefully align the emitter and receiver: orientate the receiver around the optical axis in order to set
the limits of the operation area and position the receiver approximately at the centre until the state LED
indicator on the receiver goes out.

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Job Sheet 6.1.4: Repair Mechatronics Devices and Systems – Adjusting Photoelectric
Sensor

4) Position the object to be detected between the emitter and the receiver and check that the yellow LED on
the receiver is illuminated, if the yellow LED is off, turn the trimmer anticlockwise (-) until the yellow LED
lights up: point A.

5) Remove the object and gradually turn the trimmer anticlockwise (-) until the yellow LED lights up: point B.
6) Position the trimmer half way between point A and point B in order to complete adjustment.
7) The system should then be securely fixed in place.

N. B.: The adjustment obtained in point 6 is the most efficient for obtaining maximum sensitivity in the detection of
small and semi-transparent objects; if the objects to be detected are opaque and are larger than the lens, the
trimmer should be turned to the extreme clockwise position which will allow the photoelectric sensor to operate
even in very dusty environments.

OPTICAL BRACKETS
1) Mount the optical brackets in working position and fasten it completely.
2) Supply power to the optical brackets.
3) NO SENSING OBJECT Turn the trimmer clockwise (9 full turns) to confirm the status (yellow LED is off).

4) Position the object to be sensed and check the yellow LED is on. If the yellow LED is off, turn the trimmer
anti-clockwise and find point “A” where the yellow LED is on.

5) Remove the object and turn the trimmer anti-clockwise and find point “B” where the yellow LED is on.
6) Set the trimmer to half way between points “A” and “B” for the adjustment is completed.

Code No. MAINTAIN AND REPAIR MECHATRONIC Date: Developed Date: Revised Page #
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Work Sheet 6.1.5: Repair Mechatronics Devices and Systems – Adjusting Ultrasonic
Sensor

Learning outcomes:
6 Repair Mechatronics Devices and Systems
Learning Activity:
6.1 Adjusting Ultrasonic Sensor

Instruction:
Answer ALL questions and encircle your answers using a pen (only BLUE or BLACK ink). In the event
that you have to change your previous answer to a new answer, CROSSED-OUT the former answer and
ENCIRCLE the latter answer.

1. During the calibration procedure, the sensor setting that is used to represent the minimum
sensing distance is called the
a. Range adjustment
b. Span adjustment
c. Zero adjustment

2. The span of the ultrasonic sensor is the ___________ of its setting range
a. Range adjustment
b. Span adjustment
c. Zero adjustment

3. The span current produced by a calibrated analog sensor when the target is at the maximum
distance is
a. 0
b. 4
c. 10
d. 20

4. For an analog sensor that produces an output of 0-10volts, at what distance is the target located
when it produces 2 volts if the zero calibration setting is 20 inches and the span setting is 70
inches?
a. 20 inches.
b. 30 inches.
c. 35 inches.
d. 40 inches.

5. During the calibration procedure, the sensor setting that is used to represent the maximum
sensing distance is called the
a. Range adjustment
b. Span adjustment
c. Zero adjustment

Code No. MAINTAIN AND REPAIR MECHATRONIC Date: Developed Date: Revised Page #
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